1. Field of the Invention
This invention relates to apparatus and method for correlating the geometry of a manufactured part, the geometry of a tool for manufacturing the part, and the geometry of the master design of the part toward the objectives of more efficiently making and maintaining the tool and more efficiently designing and making other tools.
2. Background Information
Dimensional accuracy of manufactured parts is a vital aspect of mass-production techniques. For example, the body of an automotive vehicle comprises a number of individual body panels that fit together. Dimensional inaccuracies in such parts may lead to poor fits that could distract from appearance and/or impair function. Such a body panel is typically a formed metal part or a formed synthetic or composite part. One example of a formed metal part is a metal stamping fabricated by metal stamping machines that perform metal stamping processes. Processes other than stamping may be used to form metal parts. Molding processes may be used to form synthetic or composite parts.
Common to such processes is the presence of a tool having a surface that imparts a similar shape to the manufactured part. Because of the nature of a particular manufacturing process, the geometry of the part may differ from that of the tool surface used to form the part. And when a new tool is first tried out, it may be discovered that the part geometry does not match that of the master design of the part.
A physical characteristic of metal is its inherent elasticity. Some metals have greater elasticity than others. Steel for example typically has greater elasticity that aluminum. Drawing a flat metal sheet to a contoured shape stretches certain local regions of the sheet beyond the elastic limit to create plastic flow of material that causes the sheet to assume the contoured shape. Other regions of the material that are stretched only within the elastic limit will relax after the draw. Such relaxation is commonly referred to as springback.
One way to draw metal is by a stamping press that contains a stamping tool. The stamping tool includes a punch on a ram of the press and a die that sits on a bed of the press. A metal sheet disposed between the punch and the die will be drawn to a formed shape when the punch and die are pressed together. The formed shape is established by the shapes of working surfaces of the punch and die.
Because of metal springback, principles of metal stamping call for a tool to impart a certain degree of overbend into a draw to compensate for springback. Because of the complex contours of some stamped parts, clear definition of the regions where springback will occur and the extent of springback in such regions are often problematic before a new tool is first tried out. Hence, the successful design of a new tool may depend more on the judgment, skills, and past experiences of its designers, rather than on detailed engineering analyses and calculations, but even at that, a new tool must be tried out.
Tool tryout has historically been a time-consuming process, typically involving a succession of various operations by skilled workers, before the new tool is able to stamp a part with the required dimensional accuracy. For example, if a punch or die is found to require additional machining, such as milling, it must be removed from a tryout press, transported to a milling machine, fixtured in the milling machine and machined, transported back to the tryout press and re-loaded, and again tried out. Newly machined areas typically require refinishing and polishing. The handling of a tool for making a body panel is often cumbersome and time-consuming because of its large size and weight. Moreover, the steps just described may have to be repeated until design intent is finally achieved.
A stamping tool has to be maintained during use. It may become worn, or even break. Tool maintenance can also consume significant amounts of time. A reworked tool may have to be tried in a tryout press before it can return to production stamping.
Apparatus and methods that improve efficiency of making and maintaining a forming tool, such as a stamping tool, will have obvious benefit to industry.
The present invention relates to apparatus and methods for improving efficiency of making and maintaining forming tools.
Certain principles of the invention involve scanning using any of various known optical shape measuring techniques. A sensor, such as an optical shape measurement camera for example, is used to record views of an object from a number of different spatial locations. Although each individual view is two-dimensional in nature, the proper number and locations of the views can collectively define a three-dimensional shape for the object with a desired degree of resolution. Processing of the scanned views by a processor, such as in a computer system running known shape measurement programming, can then define, within the accuracy of the equipment, the three-dimensional shape of the object to a desired degree of resolution.
Principles of the present invention utilize these known technologies to capture images of a tool surface and a part formed by the tool surface. The images are processed by a computer system that runs known shape measurement programming to develop a set of data defining the three-dimensional shape of the tool surface and a set of data defining the three-dimensional shape of the formed part. Each set of data is then compared with the other to disclose differences between them. Such differences are indicative of springback in the case of stamped metal. The differences may be presented in any suitable format or medium. The data may even be processed for presentation as images on a visual display such as a monitor.
In similar fashion, the shape of the part is compared to the master design for the part. Significant enough differences are indicative of a need to re-work the tool. It is believed that the use of those differences in conjunction with information derived by comparing the tool surface geometry and the formed part geometry can aid skilled tool designers and makers in determining how best to re-work the tool so that it can form parts that are fully compliant with design intent represented by the master part geometry, thereby improving efficiency of the process of making the tool.
The shape of the tool may also be compared to the master design for the part and shape of successive re-works of the tool may be compared with each other to establish relationships of how the part shape changes in consequence of changes in the geometry of the tool. This can provide data useful in any further re-work of the tool and a history that can be used in the design of other tools.
The apparatus and method for improving efficiency of tool making processes and tool maintenance processes according to the present invention arise, at least in part, through the appreciation that optical scanning can be used as a practical technique for measuring both a tool and a formed part and of the availability of computer data processing equipment that can rapidly process large amounts of data, such as that generated in implementing an optical scanning process as a step in a method for ascertaining differences between the geometry of a forming tool and a part formed by the tool.
Individual pieces of commercially available equipment that have sufficient insensitivity to the surrounding environment such as that found in and around a tool room can be used in practice of the invention.
Stated in a general way, the invention relates to apparatus and method useful in a process of making and/or maintaining a surface of a tool used to form a part. It comprises a series of steps including scanning the tool surface with an optical shape measurement camera to obtain a first set of electronic images from different views of the tool surface and processing the electronic images to develop a first set of data defining the three-dimensional shape of the tool surface. It further comprises scanning the part surface of a part made by the tool with an optical shape measurement camera to obtain a second set of electronic images from different views of a surface of the part formed by the tool surface, and processing the electronic images of the second set of images to develop a second set of data defining the three-dimensional shape of the part surface. It further comprises processing two selected sets of three sets of data to develop a fourth set of data defining differences between the two selected sets of data. The third set of data defines the master shape of the part surface.
Another aspect of the invention relates to a method of making and/or maintaining a surface of a tool used to form a part comprising scanning the tool surface with an optical shape measurement camera to obtain electronic images from different views of the tool surface, processing the electronic images to develop a first set of data defining three-dimensional shape of the tool surface, and processing the first set of data with a second set of data having a correlation with the shape of the tool surface to develop a third set of data defining differences between the first and second sets of data.
Further aspects of the invention, and its various advantages and benefits, will be seen from the following detailed description of a presently preferred embodiment of the invention.